http://en.wikipedia.org/wiki/Key_frame



Definition: An animation key frame is a single still image in an animated sequence that occurs at an important point in that sequence; key frames are defined throughout an animated sequence, in order to define pivotal points of motion before the frames in between are drawn or otherwise created to "tween" the motion between the two key frames. One example of key frames could be an animation of a swinging baseball bat; the bat at rest would be one key frame, and the bat at the end of of its swing would be another. All other frames would be "tweened" frames.



Historically, the main difficulty in creating animation has been the effort required of the animator to produce a large number of frames. One minute of animation might require between 720 and 1800 separate images, depending on the quality of the animation. Creating images by hand is a big job.

That’s where the technique of keyframing comes in.


Most of the frames in an animation are routine, incremental changes from the previous frame directed toward some goal. Traditional animation studios realized they could increase the productivity of their master artists by having them draw only the important frames, called keyframes. Assistants could then figure out what belonged on the frames in between the keyframes. The in-between frames were called tweens.

Once all of the keyframes and tweens were drawn, the images had to be inked or rendered to produce the final images. Even today, production of a traditional animation usually requires hundreds of artists to generate the thousands of images needed.

external image il_animation_traditional-2.jpgThe frames marked 1,2, and 3 are key frames. The other frames are tweens.

Look at this from

donbluthanimation.com

This is my little research about walk cycle, based on Disney's feature "Robin Hood".

http://www.donbluthanimation.com/forum/showthread.php?83-Lets-learn-Walk-cycles/page2

Here is walk cycle's key frames:


external image keyframes.jpg

The other leg works exactly the same way, so let's put it together:

external image 0000h804

It's not as smoothly as in the film, becouse we should add additional phases between the key frames

external image 0000k70t

and here is my walk cycle:

[Flash]http://img19.imageshack.us/img19/419/walk.swf[/Flash]